557 / 2019-01-18 10:52:28

NO reduction by methane reburning under oxy-fuel conditions in a jet-stirred reactor: Experiments and modeling

Reburning; NO reduction; Oxy-fuel combustion; Jet-stirred reactor

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Oxy-fuel combustion technology is one of the most promising new combustion technologies which is achieved by a strong recirculation of exhausted gases. Such a strategy implies that a high content of CO2 interact with the reactants oxidation chemistry. Reburning is a low-cost and effective NOx reduction technology that has been put into use in some combustion systems and is a promising option for both traditional and oxy-fuel combustion. In this work, new experimental results of NO reduction by CH4 in O2/N2 and O2/CO2 atmospheres were obtained in a jet-stirred reactor. The experiment was conducted at 1 atm in a temperature range of 600 K-1400 K. The equivalence ratio varied from 0.5 to 2.5. Simultaneously, the experimental conditions were simulated using an updated reaction mechanism and the experimental results showed good agreement with the simulation results. It was found that the NO reduction efficiency in the O2/CO2 atmosphere is weaker than that in the O2/N2 atmosphere. The inhibition of CH4 oxidation observed at high CO2 levels can be the reason for the lower NO reduction efficiency in an O2/CO2 atmosphere. The NO reduction in an O2/N2 atmosphere mainly passes through two paths: NO (→HCNO)→HCN→NCO→N2 and NO→HNCO→NH2→NNH→N2. While the main path of NO reduction in an O2/CO2 atmosphere is NO (→H2CN)→HCN→CH3CN→NCO→N2.
The effect of different factors on reburning in the O2/CO2 atmosphere was further studied. Different trends are found in the O2/CO2 atmosphere with an increasing temperature, the NO reduction efficiency increases first and then decreases and the maximum NO reduction is achieved at moderately high temperature. Also, the NO reduction efficiency increases first and then decreases with an increasing equivalence ratio and the maximum NO reduction is achieved near a equivalence ratio of 1.2-1.5. The NO reduction efficiency decreases and the corresponding equivalence ratio of maximum NO reduction decreases with an increase in the CO2 dilution level; Properly increasing the residence time in the O2/CO2 atmosphere can achieve greater benefits than that in O2/N2 atmosphere; With an increasing initial CH4 concentration, the NO reduction efficiency in the O2/CO2 atmosphere can reach the reduction efficiency in the O2/N2 atmosphere but a larger amount of reburning fuel is required to achieve maximum NO reduction.